This invention relates to a method of molding a deformable optic for a soft intraocular lens. More specifically, it relates to a method of molding such an optic which has an opening therein for securely receiving a haptic, which is the filamentary strand supporting the optic of the intraocular lens in the eye.
Flexible intraocular lenses which can be deformed to facilitate insertion through a small incision in the eye have steadily gained popularity in recent years. In contrast to conventional rigid intraocular lenses, for example, polymethylmethacrylate (PMMA) lenses, "soft" intraocular lenses offer advantages for ophthalmic surgeons with respect to the way in which the lens can be inserted in the eye. Since a soft intraocular lens can be folded or compressed to fit through a corneal incision having a diameter smaller than that of the soft lens in an undeformed condition, the patient receiving the intraocular lens will experience less surgical trauma and a shortened recovery period.
Although soft intraocular lenses have demonstrated numerous practical advantages for the ophthalmic surgeon, technological difficulties still remain for the preparation of these lenses. Scientists and engineers have continually worked on successfully attaching the haptic to the optic of the intraocular lens. The haptic supports the optic in the eye and therefore performs a necessary function for the successful operation of the lens. The traditional machining and staking processes for attaching the haptic to a rigid optic are inappropriate for soft optic attachment because of the flexible, deformable nature of the soft optic Numerous attempts have been made to provide methods for securely fastening the haptic to a soft optic of an intraocular lens.
U.S. Pat. Nos. 4,880,426 and 4,894,062 disclose molding the material from which the deformable optic is derived about a portion of the haptic of the intraocular lens. That portion of the haptic which is embedded within the molded optic is configured in such a manner so as to securely attach the haptic to the optic. For example, the tip of the haptic embedded in the optic may be "balled" by applying heat to the tip to soften the haptic, or the haptic may be attached to an anchoring member which may be in the form of an arcuate filamentary strand or an elongated rod. U.S. Pat. No. 4,786,445 discloses the use of laser energy to attach the haptic to a soft optic of an intraocular lens.
Although the methods described above eliminate the need to use conventional means for attaching the haptic to the optic, these methods have their drawbacks. Foremost among the problems associated with these methods is that the portion of the haptic embedded in the optic is subjected to the curing temperature required to mold the material from which the soft optic is prepared Unfortunately, the elevated temperature associated with the curing operation will cause the filamentary haptic strand to deform. This deformation may significantly affect the performance of the haptic for supporting the optic of the intraocular lens securely within the eye. It is most pronounced with haptics composed of the most commonly used materials, such as polypropylene and polymethylmethacrylate. These polymeric materials have softening temperatures which are below the temperatures required to cure the material from which the optic is made.
Therefore, in view of the deficiencies inherent in prior art methods for attaching a filamentary fixation member to a soft, deformable optic, a new method is needed for securely fastening a haptic to such an optic.